Photo for The Union by Christopher Rosacker
A 30-foot deep sinkhole formed off Highway 49 south of Grass Valley in the days following the terrential storm that dumped nearly a foot of rain on Grass Valley.

Photo for The Union by Christopher Rosacker
A 30-foot deep sinkhole formed off Highway 49, eating part of the road's shoulder, south of Grass Valley in the days following the terrential storm that dumped nearly a foot of rain on Grass Valley.

Photo for The Union by Christopher Rosacker
A 30-foot deep sinkhole formed off Highway 49 south of Grass Valley in the days following the terrential storm that dumped nearly a foot of rain on Grass Valley and swelling the small creek below where the sinkhole formed.

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A sinkhole a few miles south of Grass Valley has the potential to engulf the northbound lane of Highway 49 and close down the main route to the Sacramento area, said representatives with the California Department of Transportation.

However, Caltrans workers who discovered the growing 10-foot-wide, 30-foot-deep sinkhole were able to halt its expansion by filling it in with sand Wednesday, said Jeff Johnson, a Caltrans resident engineer.

“It’s a temporary hold to stabilize the hill,” Johnson said. “I think by stabilizing it, it will be OK.”

The sinkhole, which already swallowed a 10-foot portion of the northbound shoulder, developed above a normally babbling brook that crosses under Highway 49 through a culvert cutting through the soggy hillside.

Caltrans believes that the more than 80-year-old culvert may have a crack in it, which was exacerbated by four consecutive days of back-to-back storms that dumped nearly a foot of water on western Nevada County and peaked Sunday.

“If it keeps on going, we will have to close down the (northbound) lane,” Johnson said. “If it gets worse, we would pretty much have to close down the whole road.”

The deluge transformed that babbling brook into a flooded river, trying to drain through the same small culvert, pooling water levels 15 feet high up to the road, said Kameron Olson, an employee of the Golden Chain Motel, the entrance of which abuts the sinkhole.

Caltrans will not know the official cause until workers are able to dig down to study the hole, Johnson said.

“Right now the public is perfectly safe, and we are monitoring it,” said Caltrans spokeswoman Rochelle Jenkins.

“We have it pretty stable and it won’t spread, as long as we don’t get another four or five inches (of rain) in an hour.”

The National Weather Service expected Wednesday’s drizzles to add around two inches of precipitation to the already saturated soil and measurement as of press time supported that prediction, said Holly Osborne, a National Weather Service forecaster.

Those clouds were also expected to dissipate and give way to dry skies for the next few days, Osborne said.

“We’re looking at a dry forecast into the weekend,” Osborne said.

Repair work on the sinkhole will last for at least six weeks, located a mile north of the massive Caltrans transformation of the La Barr Meadows intersection, further slowing the commute to and from Grass Valley along the highway. More than 7,400 people are estimated to drive along Highway 49 daily, heading to work in Placer, Sacramento and other nearby counties.

Traffic will remain two lanes as long as the sinkhole does not expand, Jenkins said. The sinkhole was cordoned off from traffic Wednesday by more than 1,000 feet of heavy cement dividers.

Jenkins asked drivers to use caution in the area, drive slowly and report any unattended hazards to Caltrans.